how to get rid of fruit flies
Fruit flies are attracted and breed in many places besides fruit. They have short life spans, but long enough to lay eggs that hatch and keep swarming in and outside. The primary control for fruit flies is sanitation. Eliminate larval food and development sites. Keep fruit stored in the refrigerator. Rinse and drain bottles and cans that are to be recycled. Squeeze out mops thoroughly and dry. There may be enough food and moisture to complete development on the damp mops. Another common site is trash containers especially when they are lined with plastic bags (look between the liner and the container). Remember that the source of the infestation may not be where the adult flies are found.
Here is our website and publication for more information http://extension.umd.edu/hgic/topics/fruit-flies
If this is not what you are noticing, send us clear photos so we can see what you are dealing with. If your friend has a lot of houseplants, they may be dealing with fungus gnats. They like to breed in moist potting soil. See more http://extension.umd.edu/hgic/topics/fungus-gnats-houseplants